1. Field of the Invention
The present invention relates to an optical link module connection system, and more specifically, to an optical link module connection system for connecting an optical fiber to an optical link module which converts an optical signal to an electrical signal or vice versa.
2. Description of the Related Art
In the United States, the information superhighway is now becoming a reality. As a similar project in Japan, a fiber-optic network targeted to all subscribers is planned to be developed by 2010. The present invention will be applied to optoelectronic converters that must be one of the key devices in optical link equipment to be used by the subscribers in this project.
Optoelectronic converters, called optical link modules in general, are supplied by communications equipment manufacturers and the like, whose average production scale per supplier is presently about 100,000 modules a year. However, it is said that the fiber-optic network covering all subscribers will require a larger production scale of one million or more modules per year and intensive efforts to reduce the cost to less than 10% of the current cost. The present invention is intended to meet these challenging requirements.
FIGS. 38(A) and 38(B) are a plan and side views, respectively, showing a conventional optical link module that has a connection to an optical fiber. The optical link module shown in those figures is a pigtail type module, which is composed of an optical link module 101, an optical fiber 102 of 1-2 m in length extended therefrom, and a standard optical fiber connector 103 connected to an end of the fiber. The standard optical fiber connector 103 may be the SC connector, for example, to provide a fiber-to-fiber junction to another optical fiber cable equipped with a mating connector of the same standard.
Devices to be mounted on printed circuit boards (hereafter "PC boards") used in communications equipment are classified into the following two types in terms of mounting methods: surface mount devices and through-hole mount devices (or pin-in-hole mount devices). One of the common packages of surface mount devices is the flat pack which is often used for packaging LSIs. To mount this type of devices, a soldering process called "reflow soldering" is used as in the following sequence: printing solder paste on a bare PC board; placing surface mount devices on the printed solder paste; and soldering them on a conveyer moving through an oven heated up so that the surface temperature of the components will be 220.degree. C. or more.
On the other hand, large capacitors and LSIs provided in pin grid array (PGA) packages having many terminals over 200 pins are typical through-hole mount devices that will be mounted by using "flow soldering" techniques. That is, the leads of those devices are inserted in the through-holes bored on the PC board, and the underside (i.e., the side opposite to the component side) is then put on a solder bath that delivers molten solder heated up to about 260.degree. C. During the process of flow soldering, the temperature on the component side rises up to about 150.degree. C.
Since such surface mount devices and through-hole mount devices are mixedly mounted on the same PC boards for communication equipment, a typical factory process of automatic soldering proceeds as shown in FIGS. 39(A) to 39(E). That is, as in the sequence indicated by the subindices of the drawings, the process comprises the following steps of: (A) printing solder paste; (B) placing surface mount devices on predetermined places by using adhesion of the solder paste applied thereto; (C) applying a reflow soldering; (D) inserting the leads of through-hole mount devices into the through-holes in the predetermined places; and (E) applying a flow soldering.
In general, the optical fiber 102 extended from the optical link module 101 is coated with nylon, for example, to protect the fiber from scratches. Such coating, however, has poor heat resistance as low as 80.degree. C. and thus would melt in a high temperature in the above-described automated soldering process. Due to such temperature constraints, the optical link module 101 must be manually soldered to the PC board (cf. FIG. 40(B)) after the fellow and flow soldering processes have all finished for mounting the other components (cf. FIG. 40(A)). This exceptional work in the board assembly process will raise the manufacturing cost of the equipment.
Further, when connecting the optical fiber 102 to the optical link module 101, their optical axes must be properly aligned with each other. If it was unable to obtain a proper alignment in the first trial, the connection should be retried after cutting off a predetermined length at the end of the optical fiber 102. In preparation for this retry processing, the optical fiber 102 has an extra length that may be cut off later. Because of another requirement of minimum bending radius of 30 mm, the optical fiber 102 finally reaches 1-2 m in total length and its excessive portion is coiled up for storage. This long optical fiber is so bulky that it causes a problem with storage space and handling in the shop floor.
Lastly, the optical fiber 102 are coiled and stacked up on the PC board as shown in FIG. 41, and it also degrades the utilization factor of board space, leaving little space for mounting other parts.